import java.util.HashMap;
import java.util.Map;

public class Test5 {
    static class Num {
        int a = 10;
        int b = 20;
    }

    public static void main(String[] args) {
        Map<Num, String> map = new HashMap<>();

        Num num1 = new Num();
        map.put(num1, "hello world");
        System.out.println(num1.hashCode());
        num1.a = 30;
        System.out.println(map.get(num1));
        System.out.println(num1.hashCode());

    }
}
